1. Technical Field
The present invention relates to a transparent pixel electrode used mainly for an electrooptical device, a manufacturing method therefor, an electrooptical device having the pixel electrode, and an electronic apparatus.
2. Related Art
When forming a pixel electrode on the display side of an electrooptical device such as a liquid crystal display device, a transparent conductive film composed of indium tin oxide (ITO) or the like is used to form the pixel electrode since it is necessary to transmit light through the pixel electrode. When forming such a transparent conductive film made of ITO, vapor phase methods such as sputtering and deposition are generally used.
In the vapor phase method such as the sputtering or the like, patterning is required after forming the film, and the patterning is carried out generally using photolithography. However, the patterning using photolithography suffers high manufacturing cost and low productivity, since an extensive set of equipment such as a vacuum device is needed for the film formation and etching processes, and since the material usability is only several percent, indicating that most of the material ends up being discarded
Under the circumstances, techniques for forming the transparent conductive film by a liquid phase method are proposed. For example, the transparent conductive film is formed by: dispersing ITO microparticles in resin and an organic solvent; coating the obtained dispersion liquid by a coating method or a printing method such as dip coating, spin coating, floating, screen printing, gravure coating, or offset printing; and further drying and calcining the coated dispersion liquid (e.g., JP-A-09-194233). According to this method, since the film made particularly of the ITO microparticles has pores, a metal oxide film is formed in order to fill the pores so that gas or moisture does not readily affect the film and changes its conductivity (specific resistance).
However, when forming the transparent pixel electrodes (transparent conductive film) on the substrate side having transistors (e.g., TFTs made of amorphous silicon) formed thereon, there are problems particularly as follows.
By the coating method such as dip coating, spin coating, or floating, a mixed film of ITO microparticles and metal oxide is formed on the entire surface, and, therefore, it is not possible to carry out fine patterning (etching). This is because the ITO film is wet-etched normally using an acid-based etching liquid and patterned, while a silicon oxide as the metal oxide is wet-etched using, for example, a fluorine-based etching liquid and patterned, and, thus, there is no etching liquid that can suitably etch the mixed film of the ITO film and the silicon oxide film.
Further, by the printing method such as the screen, gravure, or offset printing, it is difficult to form a metal oxide layer on an already patterned ITO while suitably covering its side edge surfaces. If the transparent electrode (the transparent conductive film) is formed without the side edge surfaces being covered, moisture absorption occurs from the side edge surfaces of the film, and the conductivity (the specific resistance) changes. In contrast, in order to suitably cover the side edge surfaces, it is possible to thickly form the metal oxide layer. In this case, however, the surface resistance of the transparent electrode increases because of the presence of the metal oxide layer, and the transmittance of the transparent electrode decreases.